This invention relates to light modulating devices using polarized light, and more specifically to the material makeup of liquid crystal displays and polarizers.
The fabrication of a liquid crystal display (polarizer), in its simplest state, consists of a light modulating element, such as liquid crystal (polyvinyl alcohol stained with a absorbing agent such as iodine) situated between two strips of an isotropic material, typically glass. In liquid crystal displays currently in use, the structure is much more complex. A transparent electrode pattern layer, used to switch the liquid crystal from one state to another, is required. The presence of this electrode layer adds the requirement that the blocking layer be dielectric to prevent electrochemical interaction. The light modulating element of a polarizer presents a similar problem. In present application, polyvinyl alcohol is contained between two strips of an isotropic material, cellulose acetate butyrate (CAB). The CAB is not reactive with the PVA but is somewhat porous to water and other foreign substances permitting the PVA to become contaminated.
Substrate materials having anisotropic properties have not been used, as they interfered with the polarization of the light. There are available anisotropic materials having biaxial properties. One of these materials is a type of stretched polyester (plastic). This material is composed of polymer chains which are in disarray in the material's original condition. When the material is stretched, the chains are oriented lengthwise along the axis of the stretch direction. This stretching and accompanying alignment of chains defines the optical axis of the material. By careful control of the angle of the optical axes and proper alignment of the optical axes of the material with optical axis of the light modulating material, this biaxial material can be substituted for isotropic material. In addition, these plastics are very chemically stable and not likely to react with compounds used in light-modulating devices.